Thanks to "Sister Sister" star Tia Mowry we now know why some celebs can't stop Tweeting -- because they can make a bloody fortune doing it ... but Mowry claims she got bamboozled out of her earnings by a double-dealing agent.
Tia filed a lawsuit -- obtained by TMZ -- which shows she made deals to send sponsored Tweets for certain companies ... deals that were supposed to have paid her more than $108,000!!
But according to the suit ... the agent she hired to handle her Twitter deals soaked her for far more than the 10% commission to which he was entitled -- and instead took more than HALF of the Tweet deal cash.
Mowry says she's been cheated out of nearly $60K. She's suing for that, plus another $120K in punitive damages.